Hey guy’s. Been a little while. Any way’s, I felt like it was time to get this receiver going again. I don’t remember when exactly I picked it up, but it’s been in my closet for a few years now.

When I got it, It had some problems and since I didn’t know much about solid state(still don’t know a whole lot, but enough to get by, I suppose) I put it away. I remember that it had an obvious problem with the left channel. Distorted and lower on volume. I also remember it having problems with some of the inputs on it. With nothing connected, 2 of them (tape “HD”+ Phono) sound like an ocean(or a sea-shell up to your ear) at high volume. With something plugged in they are both very distorted out each channel. At that time I was thinking that it was all going to be transistor problems.

I pulled it out of the closet this last weekend, took it apart, and found that many of the electrolytic capacitors are bulging. Some of them are coming out of the wrapping on the top, while most are bulging out of the bottoms. I made a list of all the e-caps and of what boards they are on, and found that I had many of them in my stock. With the problems I had, and some troubleshooting I first figured out that my main issue stemmed at the pre-amp. So I re-capped the left half of the pre-amp. That fixed the overall problem with the left channel. Sounded great listing to the radio! I also replaced the caps on the bottom of the unit, along with 1 on the power supply that looked horrible…After that, I re-capped the rest of the pre-amp. No change in operation. I then went to the main amp board and re-capped the whole board. I checked operation a few time’s during the process. I’ve got 2 caps I want to re-change out after I get my order. The amp board had 2-500mfd cap’s and I only had 470mfd, and I’d rather have same or a slightly higher value than stock. Like I’ve been doing for the rest of the set. Though, I do believe it is sounding better than before.

Here’s my main issue though. I still have the same problems with my inputs, as I wrote about above. Where should I go from here? I know I shouldn’t touch the FM/AM board(with the alignment slugs) but should I touch the middle board on the unit? I don’t know what exactly that one is for. The crappy schematic that I’ve been loosely going off of, doesn’t list what the board does. It showed the pre-amp, main amp, FM/AM IF board, but does not name the center board (though part of that is cut off the schematic copy). I don’t want to just 'assume' that it's the input control board without knowing for sure. My AM/FM reception is great and I don’t want to mess with that.

Is there anything I should check over? Where should I go from here?....Well, besides putting in new main power supply capacitors(which I need to order).

Here's some pictures of what I'm working on:Main amp board (after re-cap)Pre-amp board (after re-cap)Center (unknown) boardAM/FM if boardFull underside shotWhat should I replace this wax cap with? Regular capacitor or an electrolytic? If the latter-Which side is +, and which is -?

These are the main output transistor's right?Well, for some reason the left side(as of this view) of the heatsink that these transistors are on, gets warm. The receiver sounds great out to the speakers though. That is the side that the rectifier is on, (behind the transformer) so maybe the heat is transferring to the heatsink?

I'll assume you don't have the service manual which probably could answer your questions.You said: "What should I replace this wax cap with? Regular capacitor or an electrolytic? If the latter-Which side is +, and which is -?"It's not an electrolytic.

Unknown board is the FM Multiplexer board.

The DF2/DF45 output transistors can get warm/very warm if the bias and resting current in each channel is not set correctly. The corresponding pots for these adjustments also tend to go bad after many years.

Preamp noises, hissing, distortion etc. generally is caused by the germanium transistors starting to deteriorate causing them to generate noise.

LR-1500T wasn't a bad design. We sold tons of them. Of course, tons of them came in for repair too. There was an early and a late model but circuitry was pretty much the same. The LR-1500TA was a slightly better design.

Check your output transistors, the emitter resistors, and the sockets for defects. The transistors can be leaky or open or shorted. If the transistor is shorted it probably opened up it's emitter resistor. The emitter and base pins of the transistors may not be making good contact in the socket. These wafer sockets sometimes loosen up on those pins. On your driver board the one on the rear with the four larger transistors on it has four pots on it. One pot for each channel to balance the D.C. operating point of the output to either half B+ or if a dual power supply to 0V. The other two pots are for setting the idle current for that channel. If these pots have a bad spot your operating conditions will change causing distortion, poor output level, output transistor and or emitter resistor failure and if the balance is off and the amplifier has dual power supplies could result in D.C. on the outputs that can damage speakers. Some sets in the day did not have a protection relay to help in this regard. Other transistors could also be bad especially those driver transistors if an output transistor failed and took it out. If your output transistor(s) are bad and the emitter resistor is open those drivers could stil be driving your speaker but at a lower level and the result would be distorted.

I seem to remember the LR1500T came out the plastic UA 703 Fairchild ICs in theFM IF. They were a disaster in the Sansui 5000. I believe the LR-1500TA changed them to the Philco PPA 7703. I wouldn't mess with that beast. If you are unhappy with the noisyphono/tape head preamp, use an outboard preamp into the aux input.

Life too short. Be happy. Stick to tubes.

UA703's were used in the 1500T and 1500TA along with a number of other Lafayette receivers and tuners. We called them UA703's, ICF-1's and, I think, some other designation. They came in metal cans and plastic. Customers blew out a lot of them. I think I still have a bag of good ones here. LR-1500T made the "best buy" two years in a row in Consumer's magazine. The front-end FM tuner used in the LR1500 receiver series and the just the tuner version model, LT-425T, were very sensitive.

So, the mystery board is the "FM Multiplexor". Hmm, so it decodes the stereo signal? If that's the case, I think i'll leave it alone unless one of you tell me I should re-cap it. My stereo fm seems to work great as is, and I don't want to mess that up...(especially if it would need re-alignment)

manualman wrote:

I'll assume you don't have the service manual which probably could answer your questions.You said: "What should I replace this wax cap with? Regular capacitor or an electrolytic? If the latter-Which side is +, and which is -?"It's not an electrolytic.

The DF2/DF45 output transistors can get warm/very warm if the bias and resting current in each channel is not set correctly. The corresponding pots for these adjustments also tend to go bad after many years.

Preamp noises, hissing, distortion etc. generally is caused by the germanium transistors starting to deteriorate causing them to generate noise.

LR-1500T wasn't a bad design. We sold tons of them. Of course, tons of them came in for repair too. There was an early and a late model but circuitry was pretty much the same. The LR-1500TA was a slightly better design.

Your assumption is correct. I've got a copy of the instruction manual with the schematic on the last couple of pages(with it having pieces missing due to improper scanning). I could not find a service manual that I could download. I think I found one for the "TA" version, but I wasn't going to bother with it.

Yea, I feel kind of dumb for having to ask about the wax cap, but I don't think ive seen one with that high of a value. That's another one i'll have to order, because the highest I keep in stock is 1mfd.

hmm, ive got to look up how to check the bias then...and then find out where it should be. Along with that resting current.

So, do the inputs all go straight to the pre-amp in a receiver? Should I find replacements for all 6 of them transistors on the pre-amp board? I was looking up the transistors that are in the pre-amp... I found that they are all well out of production, and i'd have to find modern suitable replacements. I wrote down the specs of each in my "project notebook" but how do I go about choosing one's that would work well?

How could I tell if mine is an earlier unit or a later one? That would be kind of interesting to know. I know there was about a 5 year production run, but it would be cool if I could pin point a year.

radiotechnician wrote:

I wouldn't mess with that beast. If you are unhappy with the noisyphono/tape head preamp, use an outboard preamp into the aux input.

Life too short. Be happy. Stick to tubes.

Why not I don't know... I want to actually fix this. Not just put a band aid on a problem.I love tubes, but the tube receivers are ridiculously priced, and not many can put out the power this unit does. ....or can they I suppose if someone wanted to waste thousands of dollars...

Audioman wrote:

Check your output transistors, the emitter resistors, and the sockets for defects. The transistors can be leaky or open or shorted. If the transistor is shorted it probably opened up it's emitter resistor. The emitter and base pins of the transistors may not be making good contact in the socket. These wafer sockets sometimes loosen up on those pins. On your driver board the one on the rear with the four larger transistors on it has four pots on it. One pot for each channel to balance the D.C. operating point of the output to either half B+ or if a dual power supply to 0V. The other two pots are for setting the idle current for that channel. If these pots have a bad spot your operating conditions will change causing distortion, poor output level, output transistor and or emitter resistor failure and if the balance is off and the amplifier has dual power supplies could result in D.C. on the outputs that can damage speakers. Some sets in the day did not have a protection relay to help in this regard. Other transistors could also be bad especially those driver transistors if an output transistor failed and took it out. If your output transistor(s) are bad and the emitter resistor is open those drivers could stil be driving your speaker but at a lower level and the result would be distorted.

I'm not sure how to check those output transistors. I pulled them out and ohm'd them. Got some weird and inconsistent results. Not sure what they mean, or if it is totally stupid to try to check resistance of them.I don't know what resistor's are "emitter", so no way I can check them at the moment. I did make sure the output transistor sockets were tight and cleaned with the electronics cleaner. There is actually 6 of them 'disc' pots on the driver/amp board

I only have that distortion problem with the tape hd and the phono input's. So, in that regard, I figure the amp board is fine...in that sense. I have noticed though, that right channel does have a small(quiet) hiss that can be heard with volume down. It can still be heard at max volume too, when the receiver is set to a quiet input that has nothing going through it. That has to be the main amp, as it does that on every input and doesn't change when you flip the stereo sound out set it to mono.

I'm looking at it, and it looks like all the inputs go the same path into and through the pre amp sections. With this line of logic, All of my inputs should sound bad and distorted. but! ONLY the phono and tape hd sound bad. AUX and the normal tape in sound great-though is a little lower in volume compared to the tuner.

Oh, and after several hours now of frustration, how do I figure out replacements for my transistor's? I can't find any when I try to look up modern versions using the specifications of the old one's.

Old ones(all on pre-amp):2SB3482SC2812SB324

Should I trust the clear caps? I have 2 of each 1000, 1600, and 2200 on my pre-amp board. I found (somewhere else) that they are not to be trusted in electronic equipment if there is problems.

I also left a pair of 3.3mfd 25v. capacitors on the pre-amp boards. Should I change these out? I didn't change them because they are odd looking little electrolytic's, yellow in color.

It's an unusual circuit. The signal is routed to the same input stage regardless of source, then another switch section controls the feedback loop to set the gain and eq for each source. This means that your transistors are OK.

What are you using for a signal source to check the phono and tape head inputs? These inputs expect very low level signals, only a few millivolts. When they indicate Tape Head, they mean right off the head, no preamp.

Take the signal source that you were using to find no distortion on the AUX input,and connect a one megohm resistor in series with the phono plug .

Try that plugged that into the tape and phono jacks.

I did log into HIFI engine (after 3 1/2 years) and have schematic now.

The three transistors in each channel are direct coupled.

I may have specs on those. ....looking... but if they ain't broke......

Ok, i'll give that a try and see what happens.

I've already got the specs for the transistors. That actually wasn't too hard to find, then I wrote them down in the "project notebook". Its a bit much to re-write though, unless necessary.

dberman51 wrote:

It's an unusual circuit. The signal is routed to the same input stage regardless of source, then another switch section controls the feedback loop to set the gain and eq for each source. This means that your transistors are OK.

What are you using for a signal source to check the phono and tape head inputs? These inputs expect very low level signals, only a few millivolts. When they indicate Tape Head, they mean right off the head, no preamp.

-David

Oh, that is great to read! It's got to be something farther than those transistors, that only phono and tape hd go through. hmm, maybe I should print out this schematic and actually (physically) highlight the path. Might make it easier for me to find something that could be off.

I have now used a turntable, my ipod touch (through converter cable-1.5mm to RCA cable ends) and a tape deck. No change between them- all plenty distorted. I will also state that there is noise with nothing connected to these inputs when the unit is set to them. Sounds sort of like and ocean through the headphones. Well... it was the same through speakers too.

OK, I think the problem is becoming clear. There may be nothing wrong with the amplifier. You may be drastically overdriving the inputs. An iPod will blast the PHONO and TAPE HEAD inputs something terrible.

The PHONO input is for a magnetic cartridge only. If your turntable has a ceramic cartridge that will severely overdrive the inputs. If the turntable sounds OK using the AUX input that guarantees it has a ceramic cartridge and will overdrive the PHONO input.

If this is the case, get a proper turntable with a magnetic cartridge and try it. It should sound excellent through the PHONO input. You can try it through the TAPE HEAD input and it should sound somewhat muddy, as the eq is different.

It is normal for these old solid-state preamps to hiss like crazy when the low-level inputs are unterminated. They are intended to be terminated by a low-impedance source, i.e magnetic phono cartridge or tape head, both of which are coils. If you short the input to ground the hiss should go away. If this is what's happening, that's normal.

Not again... This is starting to sound like the issue I had with my Realistic STA-430, which was operator error. At that time, I wanted to run my 8-track player through the unused phono input. It came out sounding really distorted, and for the longest time, I thought it was my Realistic 8-track player.Only thing different though, was that the amp didn't make any sound when nothing was connected to phono, unlike the Lafayette here.

Ah, how I hate wasting time Well, thanks for the help so far guy's, even with it possibly being to my stupidity/ignorance with this old of an receiver.

Anyway's...The turntable cartridge is a Shure R25XT. I don't know if it's magnetic or moving coil...or even ceramic. I should also mention that the turntable I tested it on, is currently modified for the 5.1 surround sound system it's connected to. I (quite awhile ago) installed a Pyle pre-amp inside the case so it would produce volume from the crappy 5.1 system.

If the Lafayette can only handle signal directly from the cartridge, I now see why it would sound bad. I'm going to try it later on my JVC turntable connected to the main stereo. That doesn't have a pre-amp in the way. Still doesn't explain the "hiss" I have with nothing connected. I don't have any other receivers that do that. Is that just something about these old (late 60's-early 70's) units?

The tape deck is the one that came with the receiver: Lafayette RK-760It works fine in the regular tape input/output. I don't know what the circuitry consists of inside the player, but it is more than just the output connected to the tape head.

Can I use that "tape hd" input for anything? Can it easily be modded to be another aux? Same question/comment as above, regarding the hiss as well.

I didn't think the ipod would have strong enough signal to actually overdrive anything.

and YES, Hiss completely goes away if I short the inputs to ground.

I just read that last comment you made David. I guess that answer's my question about the hiss.

Your Pyle preamp is intended to drive an AUX input, not a PHONO input. PHONO inputs are for direct connection to a magnetic cartridge. Most 5.1 systems don't have PHONO inputs so you have to use an external preamp, but all hi-fi receivers do.

And no, you can't use the TAPE HEAD input for anything. In the early to mid 1960s, Lafayette sold very inexpensive ($30-70) reel-to-reel reproduce-only tape decks, specifically to play pre-recorded 4-track stereo tapes. They were nothing but a bare transport and play head, no electronics of any kind. So they required a reproduce preamp which the TAPE HEAD input provides. These tape decks were never any good and they're all gone now. Your Lafayette tape recorder has record and reproduce amplifiers, and is intended for connection to the TAPE MONITOR inputs.

So you can button the receiver up, polish it, place it in service, and go on to the next project.